Image coding apparatuses record image data to be broadcasted via digital broadcasting or the like into recording media such as DVDs or the like by using image coding techniques such as MPEG2, H.264, or the like. The image coding apparatuses perform a code amount control process on the basis of recording conditions such as capacity of recording media, recording time, or the like.
Non-Patent Document 1 shows TM5 (Test Model 5) which is one of code amount control methods. The TM5 is a technique proposed in the process of standardization of MPEG2 coding scheme.
The TM5 performs the code amount control by using a characteristic value of image data, which is referred to as activity. The activity is a characteristic value indicating the complexity of an image. The activity of a macroblock, for example, is calculated by the following procedure. A differential absolute value between a pixel value of each of pixels in a macroblock and an average pixel value of the pixels in the macroblock is calculated, and then a sum total of the differential absolute values of all the pixels in the macroblock is calculated as the activity of the macroblock.
Patent Document 1 discloses a technique for detecting a scene change on the basis of the activity of image data.